Heim > Artikel > Web-Frontend > Verwenden Sie JavaScript und Canvas, um Bilder zuzuschneiden
In diesem Artikel wird hauptsächlich die Methode zur Verwendung von JavaScript + Canvas zum Zuschneiden von Bildern vorgestellt.
Canvas ist ein Tag, mit dem wir Skriptzeichnungen verwenden können von Eigenschaften und Methoden. Damit können wir Grafikzeichnungen, Bildverarbeitung und sogar einfache Animationen und Spiele produzieren.
Das Canvas-Tag hat nur zwei Attribute: Breite und Höhe, die zum Festlegen der Breite und Höhe der Leinwand verwendet werden. Wenn sie nicht über Tag-Attribute oder Skripte festgelegt werden, ist der Standardwert 300*150;
Okay Okay, hier ist zuerst die Einführung in Canvas. Schauen wir uns den Code zum Zuschneiden von Bildern mit Javascript in Kombination mit Canvas an:
var selectObj = null; function ImageCrop(canvasId, imageSource, x, y, width, height) { var canvas = $("#" + canvasId); if (canvas.length == 0 && imageSource) { return; } function canvasMouseDown(e) { StopSelect(e); canvas.css("cursor", "default"); } function canvasMouseMove(e) { var canvasOffset = canvas.offset(); var pageX = e.pageX || event.targetTouches[0].pageX; var pageY = e.pageY || event.targetTouches[0].pageY; iMouseX = Math.floor(pageX - canvasOffset.left); iMouseY = Math.floor(pageY - canvasOffset.top); canvas.css("cursor", "default"); if (selectObj.bDragAll) { canvas.css("cursor", "move"); canvas.data("drag", true); var cx = iMouseX - selectObj.px; cx = cx < 0 ? 0 : cx; mx = ctx.canvas.width - selectObj.w; cx = cx > mx ? mx : cx; selectObj.x = cx; var cy = iMouseY - selectObj.py; cy = cy < 0 ? 0 : cy; my = ctx.canvas.height - selectObj.h; cy = cy > my ? my : cy; selectObj.y = cy; } for (var i = 0; i < 4; i++) { selectObj.bHow[i] = false; selectObj.iCSize[i] = selectObj.csize; } // hovering over resize cubes if (iMouseX > selectObj.x - selectObj.csizeh && iMouseX < selectObj.x + selectObj.csizeh && iMouseY > selectObj.y - selectObj.csizeh && iMouseY < selectObj.y + selectObj.csizeh) { canvas.css("cursor", "pointer"); selectObj.bHow[0] = true; selectObj.iCSize[0] = selectObj.csizeh; } if (iMouseX > selectObj.x + selectObj.w - selectObj.csizeh && iMouseX < selectObj.x + selectObj.w + selectObj.csizeh && iMouseY > selectObj.y - selectObj.csizeh && iMouseY < selectObj.y + selectObj.csizeh) { canvas.css("cursor", "pointer"); selectObj.bHow[1] = true; selectObj.iCSize[1] = selectObj.csizeh; } if (iMouseX > selectObj.x + selectObj.w - selectObj.csizeh && iMouseX < selectObj.x + selectObj.w + selectObj.csizeh && iMouseY > selectObj.y + selectObj.h - selectObj.csizeh && iMouseY < selectObj.y + selectObj.h + selectObj.csizeh) { canvas.css("cursor", "pointer"); selectObj.bHow[2] = true; selectObj.iCSize[2] = selectObj.csizeh; } if (iMouseX > selectObj.x - selectObj.csizeh && iMouseX < selectObj.x + selectObj.csizeh && iMouseY > selectObj.y + selectObj.h - selectObj.csizeh && iMouseY < selectObj.y + selectObj.h + selectObj.csizeh) { canvas.css("cursor", "pointer"); selectObj.bHow[3] = true; selectObj.iCSize[3] = selectObj.csizeh; } if (iMouseX > selectObj.x && iMouseX < selectObj.x + selectObj.w && iMouseY > selectObj.y && iMouseY < selectObj.y + selectObj.h) { canvas.css("cursor", "move"); } // in case of dragging of resize cubes var iFW, iFH, iFX, iFY, mx, my; if (selectObj.bDrag[0]) { iFX = iMouseX - selectObj.px; iFY = iMouseY - selectObj.py; iFW = selectObj.w + selectObj.x - iFX; iFH = selectObj.h + selectObj.y - iFY; canvas.data("drag", true); } if (selectObj.bDrag[1]) { iFX = selectObj.x; iFY = iMouseY - selectObj.py; iFW = iMouseX - selectObj.px - iFX; iFH = selectObj.h + selectObj.y - iFY; canvas.data("drag", true); } if (selectObj.bDrag[2]) { iFX = selectObj.x; iFY = selectObj.y; iFW = iMouseX - selectObj.px - iFX; iFH = iMouseY - selectObj.py - iFY; canvas.data("drag", true); } if (selectObj.bDrag[3]) { iFX = iMouseX - selectObj.px; iFY = selectObj.y; iFW = selectObj.w + selectObj.x - iFX; iFH = iMouseY - selectObj.py - iFY; canvas.data("drag", true); } if (iFW > selectObj.csizeh * 2 && iFH > selectObj.csizeh * 2) { selectObj.w = iFW; selectObj.h = iFH; selectObj.x = iFX; selectObj.y = iFY; } drawScene(); } function canvasMouseOut() { $(canvas).trigger("mouseup"); } function canvasMouseUp() { selectObj.bDragAll = false; for (var i = 0; i < 4; i++) { selectObj.bDrag[i] = false; } canvas.css("cursor", "default"); canvas.data("select", { x: selectObj.x, y: selectObj.y, w: selectObj.w, h: selectObj.h }); selectObj.px = 0; selectObj.py = 0; } function Selection(x, y, w, h) { this.x = x; // initial positions this.y = y; this.w = w; // and size this.h = h; this.px = x; // extra variables to dragging calculations this.py = y; this.csize = 4; // resize cubes size this.csizeh = 6; // resize cubes size (on hover) this.bHow = [false, false, false, false]; // hover statuses this.iCSize = [this.csize, this.csize, this.csize, this.csize]; // resize cubes sizes this.bDrag = [false, false, false, false]; // drag statuses this.bDragAll = false; // drag whole selection } Selection.prototype.draw = function () { ctx.strokeStyle = '#666'; ctx.lineWidth = 2; ctx.strokeRect(this.x, this.y, this.w, this.h); // draw part of original image if (this.w > 0 && this.h > 0) { ctx.drawImage(image, this.x, this.y, this.w, this.h, this.x, this.y, this.w, this.h); } // draw resize cubes ctx.fillStyle = '#999'; ctx.fillRect(this.x - this.iCSize[0], this.y - this.iCSize[0], this.iCSize[0] * 2, this.iCSize[0] * 2); ctx.fillRect(this.x + this.w - this.iCSize[1], this.y - this.iCSize[1], this.iCSize[1] * 2, this.iCSize[1] * 2); ctx.fillRect(this.x + this.w - this.iCSize[2], this.y + this.h - this.iCSize[2], this.iCSize[2] * 2, this.iCSize[2] * 2); ctx.fillRect(this.x - this.iCSize[3], this.y + this.h - this.iCSize[3], this.iCSize[3] * 2, this.iCSize[3] * 2); }; var drawScene = function () { ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height); // clear canvas // draw source image ctx.drawImage(image, 0, 0, ctx.canvas.width, ctx.canvas.height); // and make it darker ctx.fillStyle = 'rgba(0, 0, 0, 0.5)'; ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height); // draw selection selectObj.draw(); canvas.mousedown(canvasMouseDown); canvas.on("touchstart", canvasMouseDown); }; var createSelection = function (x, y, width, height) { var content = $("#imagePreview"); x = x || Math.ceil((content.width() - width) / 2); y = y || Math.ceil((content.height() - height) / 2); return new Selection(x, y, width, height); }; var ctx = canvas[0].getContext("2d"); var iMouseX = 1; var iMouseY = 1; var image = new Image(); image.onload = function () { selectObj = createSelection(x, y, width, height); canvas.data("select", { x: selectObj.x, y: selectObj.y, w: selectObj.w, h: selectObj.h }); drawScene(); }; image.src = imageSource; canvas.mousemove(canvasMouseMove); canvas.on("touchmove", canvasMouseMove); var StopSelect = function (e) { var canvasOffset = $(canvas).offset(); var pageX = e.pageX || event.targetTouches[0].pageX; var pageY = e.pageY || event.targetTouches[0].pageY; iMouseX = Math.floor(pageX - canvasOffset.left); iMouseY = Math.floor(pageY - canvasOffset.top); selectObj.px = iMouseX - selectObj.x; selectObj.py = iMouseY - selectObj.y; if (selectObj.bHow[0]) { selectObj.px = iMouseX - selectObj.x; selectObj.py = iMouseY - selectObj.y; } if (selectObj.bHow[1]) { selectObj.px = iMouseX - selectObj.x - selectObj.w; selectObj.py = iMouseY - selectObj.y; } if (selectObj.bHow[2]) { selectObj.px = iMouseX - selectObj.x - selectObj.w; selectObj.py = iMouseY - selectObj.y - selectObj.h; } if (selectObj.bHow[3]) { selectObj.px = iMouseX - selectObj.x; selectObj.py = iMouseY - selectObj.y - selectObj.h; } if (iMouseX > selectObj.x + selectObj.csizeh && iMouseX < selectObj.x + selectObj.w - selectObj.csizeh && iMouseY > selectObj.y + selectObj.csizeh && iMouseY < selectObj.y + selectObj.h - selectObj.csizeh) { selectObj.bDragAll = true; } for (var i = 0; i < 4; i++) { if (selectObj.bHow[i]) { selectObj.bDrag[i] = true; } } }; canvas.mouseout(canvasMouseOut); canvas.mouseup(canvasMouseUp); canvas.on("touchend", canvasMouseUp); this.getImageData = function (previewID) { var tmpCanvas = $("<canvas></canvas>")[0]; var tmpCtx = tmpCanvas.getContext("2d"); if (tmpCanvas && selectObj) { tmpCanvas.width = selectObj.w; tmpCanvas.height = selectObj.h; tmpCtx.drawImage(image, selectObj.x, selectObj.y, selectObj.w, selectObj.h, 0, 0, selectObj.w, selectObj.h); if (document.getElementById(previewID)) { document.getElementById(previewID).src = tmpCanvas.toDataURL(); document.getElementById(previewID).style.border = "1px solid #ccc"; } return tmpCanvas.toDataURL(); } }; } function autoResizeImage(maxWidth, maxHeight, objImg) { var img = new Image(); img.src = objImg.src; var hRatio; var wRatio; var ratio = 1; var w = objImg.width; var h = objImg.height; wRatio = maxWidth / w; hRatio = maxHeight / h; if (w < maxWidth && h < maxHeight) { return; } if (maxWidth == 0 && maxHeight == 0) { ratio = 1; } else if (maxWidth == 0) { if (hRatio < 1) { ratio = hRatio; } } else if (maxHeight == 0) { if (wRatio < 1) { ratio = wRatio; } } else if (wRatio < 1 || hRatio < 1) { ratio = (wRatio <= hRatio ? wRatio : hRatio); } else { ratio = (wRatio <= hRatio ? wRatio : hRatio) - Math.floor(wRatio <= hRatio ? wRatio : hRatio); } if (ratio < 1) { if (ratio < 0.5 && w < maxWidth && h < maxHeight) { ratio = 1 - ratio; } w = w * ratio; h = h * ratio; } objImg.height = h; objImg.width = w; }
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